1. Field of the Invention
The present invention relates to a method for controlling a laser light power used in writing data into an optical disc, a method for verifying data written in an optical disc, an optical disc recording apparatus for writing data while controlling a laser light power, and an optical disc recording apparatus capable of verifying data written in an optical disc.
2. Description of Related Art
A phase-change based optical disc has been proposed into and/or from which data is written by irradiating a laser light onto the optical disc.
The phase-change optical disc comprises a transparent substrate made of a plastic material such as polycarbonate and having a main side thereof covered with a multiple layer made of a plurality of functional layers including a phase-change material layer.
Data write and/or read is done onto and/or from the multiple layer as a recording surface by making use of the difference in reflectivity between crystalline and amorphous phases of the phase-change material in the phase-change layer.
More particularly, data is written as a pattern consisting of spaces formed in the crystalline phase of the phase-change material and marks formed in the amorphous phase, both along a track on the recording surface when irradiated with a laser light having a controlled power.
For writing such marks, a laser light is irradiated onto the recording surface to heat a region, within a focused spot of the laser light, of the phase-change material layer to a temperature above its melting point. The phase-change material layer region is changed to an amorphous phase by quenching.
Also, for writing spaces, a laser light is irradiated onto the recording surface to heat a region, within a focused spot of the laser light, of the phase-change material layer to a temperature above its crystallizing point and below its melting point, to thereby crystallize the phase-change material layer region within the focused laser spot.
Also, for data reading, a laser light is irradiated onto the recording surface to detect a difference in return amount between the reflected portions of a laser light from the spaces and marks thus written in order to read data from the optical disc.
Unlike the magneto-optic disc, the phase-change optical disc needs no application of any external magnetic field for data write and/or read. Namely, it needs no magnetic head or the like for data write and/or read. The phase-change optical disc has been researched and developed as a data recording media of a next generation.
For forming spaces and marks on the recording surface of a phase-change optical disc, it is necessary to irradiate onto the recording surface a laser light having a power corresponding to each of the spaces and marks, respectively.
Conventionally, a laser light of a preset power is used. For this reason, the system margin for a phase change of the phase-change material and the like in a phase-change optical disc is small.
Also, a so-called verification is effected of data written with spaces and marks on the recording surface of a phase-change optical disc as the case may be.
Conventionally, the above verification is effected as a separate step after writing a series of data. Therefore, the verification takes a certain time, and there has been no way to complete the verification in a shorter time, which has been one of the causes of the low data transfer rate in the phase-change recording technology.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing laser light power controlling method for optimizing a laser light power while writing data into a phase-change optical disc, and an optical disc verifying method for verifying data written in a phase-change optical disc while writing further data into the optical disc.
Also, the present invention has another object to provide an optical disc recording apparatus adapted to optimize a laser light power while writing data, and an optical disc recording apparatus adapted to verify data written in a phase-change optical disc while writing further data into the optical disc.
The above object can be accomplished by providing a laser light power controlling method, comprising, according to the present invention, the steps of irradiating onto an optical disc a laser light generated by a laser source driven under a data write signal; detecting a reflected portion of a laser light irradiated onto the optical disc; and detecting an undershoot of a detection signal of the reflected laser light and controlling the power of the laser light correspondingly to the amount of the detected undershoot.
With this laser light power controlling method, it is possible to optimize the laser light power while writing data into the optical disc. Therefore, this method can support optical discs having various characteristics. Also this method allows a large system margin.
Also, the above object can be accomplished by providing a method for writing data into an optical disc, comprising, according to the present invention, the steps of irradiating onto an optical disc a laser light generated by a laser source driven under a data write signal; detecting a reflected portion of the laser light irradiated onto the optical disc; and detecting an undershoot of a detection signal of the reflected laser light and discriminating the level of the undershoot based on a predetermined threshold.
This optical disc verifying method permits to verify data written in an optical disc while writing further data into the optical disc. Therefore, no separate step of verifying such data written in the optical disc is necessary, which dedicates to improve the data transfer rate and the like.
Further, the above object can be accomplished by providing an optical disc recording apparatus, comprising, according to the present invention, means of irradiating a laser light onto an optical disc correspondingly to a data write signal; a photodetector to detect a reflected portion of the laser light irradiated onto the optical disc; and an undershoot detector to detect an undershoot of a detection signal of the laser light detected by the photodetector; the power of the laser light being controlled based on the amount of the detected undershoot.
This optical disc recording apparatus is adapted to simultaneously optimize the laser light power while writing data into an optical disc and verify data written in the optical disc. Therefore, the optical disc recording apparatus contributes to attain a high speed of data processing.